This invention relates generally to storage and dispensing systems for the selective dispensing of fluids from a vessel in which the fluid components are sorptively retained by a solid sorbent medium, and are desorptively released from the sorbent medium in the dispensing operation. More specifically, this invention relates to a storage and dispensing system of a type which provides superior gas purities from adsorbent based gas delivery systems.
The objective of the present invention is to provide superior gas purities from adsorbent based gas delivery systems. Currently, adsorbent based gas delivery systems are used, for example, in the semiconductor industry as a means of supplying hazardous gases in a safe manner. This is currently achieved by adsorbing the hazardous gas on an adsorbent substrate. The gas is then removed (desorbed) by applying vacuum to the system. In this type of system, impurities can also be co-desorbed during the gas removal phase. The impurities may originate either from the adsorbent media, the vessel package, or from the source gas itself. The present invention integrates a purifier with the adsorbent based delivery system so that any impurities that may be present in the system are removed from the gas prior to the gas exiting the vessel. In the semiconductor industry, for example, this is particularly important because gas phase impurities can contaminate the semiconductor device during manufacture and possibly lead to a reduction in device yield.
Toxic and other hazardous specialty gases are used in a number of industrial applications, including semiconductor device fabrication. Many users of these hazardous specialty gases are concerned about the possibility of an unintentional release. By virtue of having a positive gauge pressure, pressurized gases in cylinders will be released immediately once a shut-off valve attached to the pressurized cylinder is opened. Even with a gas-tight outlet cap in place (as required for most hazardous gases), unintentional opening of the valve can lead to serious consequences when the cap is removed. Although always undesirable, a hazardous gas release may be particularly undesirable in semiconductor processing applications. Such a release would necessitate a partial or complete evacuation of the semiconductor processing factory, leading to substantial losses in scrap product and unscheduled downtime. Also, the sensitive and expensive equipment used in semiconductor processing factories may be damaged by exposure to even traces of the hazardous gas. Adsorbent based gas delivery systems are one type of system currently used to provide hazardous gases safely.
For example, Knollmueller (U.S. Pat. No. 4,744,221) describes a process of adsorbing a gas onto a solid sorbent so that the equilibrium pressure of the gas is reduced inside of a vessel. By heating the vessel, the equilibrium pressure in the vessel could be increased and permit the delivery of the gas at above-atmospheric pressure.
In their “SDS” system, Tom, et al. (U.S. Pat. No. 5,518,528 and subsequently U.S. Pat. Nos. 5,704,965 and 5,704,967) improved on this concept by using a sorbent where the gas could be released without substantial decomposition by reducing the downstream pressure. Here, a process and apparatus is disclosed which includes a vessel that holds a solid-phase sorbent medium at pressure, a sorbate gas physically adsorbed on the sorbent medium, and a dispensing assembly that provides desorbed gas at a pressure below that of the interior pressure of the vessel. No provision is disclosed concerning the purification of the desorbed gas inside the vessel. These applications are fully incorporated by reference herein.
Additionally, Zheng (U.S. Pat. No. 5,409,526) discloses a cylinder having a valve with two internal ports. One internal port is used to fill the cylinder while the other is fitted with a unit which removes particulates and impurities from the gas as it leaves the cylinder. The unit comprises an inlet, a first filter for removing coarse particulates, layers of adsorbent for removing impurities, and a second filter for removing fine particulates. This system, however, is not an adsorbent based system.
Tom (U.S. Pat. No. 5,761,910) teaches a system for the storage and on-demand dispensing of a fluid that is sorbable on a physical sorbent. Subsequent to sorption, the fluid is desorbable from the sorbent by pressure mediated desorption and/or thermally-mediated desorption. No provision is made to purify the gas exiting the vessel within the vessel.
Olander (U.S. Pat. No. 5,851,270) discloses a gas storage and dispensing system in which a gas is sorptively retained on a bed of physical adsorbent material in a containment vessel. Gas is desorbed for selective dispensing from the vessel. A gas-flow resistance-reducing structure such as a gas-permeable porous tube, inert packing, or dispersed inert material is provided within the vessel to reduce the resistance to flow of desorbed gas from the bed of adsorbent material during the dispensing operation. Again, no provision is made to purify the gas exiting the vessel within the vessel.
In the past, most efforts have focused on either purifying the gas after it exits the adsorbent based gas delivery system, improving the purity of the fill gas, or tightly controlling the quality of the adsorbent media. It is not believed that any patents exist on improving the purity of the adsorbent based gases, and no prior attempt has been made to purify the desorbed gas in a device inside the container vessel.
It is principally desired to provide an adsorbent based gas delivery system with an integral purifier.
It is further desired to provide an adsorbent based gas delivery system with an integral purifier that costs less than the cost of an adsorbent based gas delivery system with a separate purifier.
It is further desired to provide an adsorbent based gas delivery system with an integral purifier where the purifier is integral with the vessel such that appropriate amounts of purification media can be provided for the gas delivery system vessel where the media will not become exhausted due to, for example, use on other vessels.
It is still further desired to provide an adsorbent based gas delivery system with an integral purifier that includes provision to add gas to the gas storage vessel of the system without having the gas pass through the purifier when entering the vessel during filling.
Finally, it is desired to provide an adsorbent based gas delivery system with an integral purifier where sources of leaks of hazardous gases from fittings and valving typically required for an external purifier are minimized.